Electrochemical process for the production of organometallic compounds



Jan. 21, 1964 J. LINSK 3,118,825

ELECTROCHEMICAL PROCESS FOR THE PRODUCTION OF ORGANOMETALLIC cou ounns Filed June 9, 1960 INVEN TOR.-

Jack 1/;

AT T 0/?NE Y United States Patent 3,113,825 ELEtJTROCHEMlCAL PRUCESS FQR THE PRODUC- TION OF fiRGANflMiETALll (IOWEP'OUNDS .laelr Linsk, Highland, ind, assignor to Standard Oil Company, Chicago, llll, a corporation of Indiana Filed June 9, 1964 Ser. No. 35,078 17 Claims. (tCl. Mid-59) This invention relates to organometallic compounds and more particularly concerns improvements in an electrolytic process for preparing tetra-alkyl lead compounds such as tetraethyl lead or tetramethyl lead.

Tetraethyl lead, and now tetramethyl lead, are important organometallic compounds of commerce. Many processes have been devised for their manufacture, although few have been commercially satisfactory.

Recently, it was discovered that tetra-alkyl lead compounds such as tetraethyl lead may be prepared by electrolyzing an alkyl Grignard reagent, e.g., ethyl magnesium chloride, using a lead anode. By this electrolysis, alkyl groups on the Grignard reagent are transferred to the lead anode, forming tetra-alkyl lead and giving magnesium chloride as a by-product. This electrolytic process is vastly superior to purely chemical processes by reason of the low investment and reaction materials costs, particularly as applied to small plants.

Unfortunately, this electrolytic process presents certain operational difiiculties, chiefly in the recovery of tetra alkyl lead from the electrolysis reaction mixture. The particular ethers which are technically attractive as Grignard reagent solvents are susceptible to chemical attack by the reagents at elevated temperature. Since these ethers are frequently expensive materials, it is essential to provide a tetra-alkyl lead compound recovery process which reduces the opportunity for ether decomposition.

In accordance with the invention, the electrolytic reaction mixture from electrolysis of an alkyl Grignard reagent with a lead anode and employing a dialkyl ether of an ethylene glycol having fewer than three ethylene groups in the glycol portion and having at least two carbon atoms in each alkyl group as Grignard reagent solvent, is treated for recovery of the tetra-alkyl lead compound by (l) separating the reaction mixture into a first liquid phase containing unconverted Grignard reagent, a minor portion of the tetra-alkyl lead compound, magnesium halide and ether from a second liquid phase containing substantially only tetra-alkyl lead compound and ether, (2) extracting tetra-alkyl lead compound from the first liquid phase with a selective solvent chosen from the group consisting of paraffins and dialkyl ethers of ethylene glycols having fewer than three ethylene groups in the glycol portion, and mixtures thereof, (3) recovering tetra-alkyl lead compound from the extract, and (4) recovering additional tetra-alkyl lead compound from the second liquid phase. The foregoing recovery steps advantageously comprise distillation, preferably either vacuum or steam distillation to maintain relatively low temperatures. It will be particularly noted that at no stage of the inventive process is alkyl Grignard reagent heating in contact with the ether, thus minimizing or eliminating entirely any opportunities for decomposition of the latter by the former.

in one aspect of the invention, when the extracting solvent comprises a parafiin, the paraffin is an alkane or cycloalkane which boils below the boiling point of the particular tetra-alkyl lead compound produced. In this event, tetra-alltyl lead may be recovered from the extract by distillation.

In another aspect of the invention, when the extracting solvent'comprises a dialkyl ether of an ethylene glcol having fewer than three ethylene groups in the glycol portion, tetra-alkyl lead recovery from the extract is readily accomplished by low temperature distillation, either under 3,113,825 Patented Jan. 21, 1964 vacuum or in the presence of steam. With this class of solvents, the identical solvent employed for the electrolysis may be the solvent for extraction, and accordingly the tetra-alkyl lead compound content of both the second liquid phase and the extract may be recovered simultaneously in the same distillation. This procedure has obvious advantages in terms of equipment savings.

The invention will be described in detail, and further advantages thereof will become apparent, from the ensuing description when read in conjunction with the attached drawing wherein:

FlGURE 1 schematically shows a flow sheet of a process for preparing a tetra-alkyl lead compound by electrolyzing an alkyl Grignard reagent, recovering the tetra-alkyl lead compound by separating the electrolysis reaction mixture into two liquid phases, and extracting the tetra-alkyl lead compound from the phase containing unreacted Grignard reagent, tetra-alkyl lead compound, magnesium halide etherate, and ether with a paraflin solvent; and

FIGURE 2. schematically shows a process wherein the electrolysis and separation steps are similar to those of FIGURE 1 but extraction is effected with a dialkyl ether of an ethylene glycol having fewer than three ethylene groups in the glycol portion.

It will be evident that many auxiliary utilities, duplicate items of equipment, and other details have been omitted from the figures for purposes of overall clarity and simplicity. However, those skilled in the relevant arts will have no difficulty in recognizing the need for and location of such apparatus as pumps, heat exchangers, valves, and the like.

Before commencing with the discussion of the respective process flow sheets, the overall electrolytic process is best considered. Fundamentally, the electrolytic reaction may be represented by the formula:

2RM X+2RX+Pb- PbR,+2M X where R represents an alkyl group, which may be the same or different alkyl groups in the formula, and where ethylene groups in the glycol portion and having at least two carbon atoms in each alkyl group. Thus, the suitable ethers have the formula, R-O(C H O) -R, wherein each R has at least two and advantageously not more than about ten carbon atoms in an alltyl group, and small 11 is one or two. The glycol ethers outside of the foregoing formula tend to form a magnesium halide etherate which precipitates out of the ether solution; glycol etherates within the formula defined above remain in solution and do not plug and foul equipment. Suitable glycol ethers are available commercially under the tradenames Cellosolves, wherein n is one, and Carbitols, wherein n is two. Examples of these Cellosolves and Carbitols together with their normal boiling points are diethyl Cellosolve (1l8l20 C.), dibutyl Cellosolve (204 C.), diethyl Carbitol (188 C.), dibutyl Carbitol (255 C.), and hexylethyl Carbitol (258 0.). The optimum glycol ether will depend on the particular tetra-alkyl lead compound being prepared; advantageously the glycol ether has a higher boiling point than the tetra-alkyl lead compound. For example, tetramethyl lead boils at C., and consequently any of the Cellosolves may be employed, while tetraethyl lead boils at C. (with some decomposition) and consequently the higher boiling Cellosolves are preferred. It will be understood however that glycol ethers may be chosen which boil at lower temperatures than the tetra-alkyl lead compound, in which event a distillative separation will result in the glycol ether be- '3 ing obtained as an overhead product while the tetra-alkyl lead compound is taken as a bottoms material.

A special advantage of electrolytic tetra-alkyl lead processes is that they may be employed to manufacture a wide variety of tetra-alkyl lead compound. Thus, tetramethyl lead, tetraethyl lead, tetra-iso-butyl lead, dimethyl-diethyl lead, trimethyl-ethyl lead, and other allryl lead compounds may be prepared. At present, only the tetraethyl and tetramethyl lead compounds are commercially desirable.

The electrolyte before electrolysis commences advantageously contains the particular alkyl Grignard reagent at a concentration within the range of about 1.53.5 Normal, preferably within the range of about 22.5 Normal, and additionally contains excessive alkyl halide.

The presence of excessive alkyl halide, over and above that necessary for the stoichiometric reaction, simultaneously afiords several benefits; it reacts with magnesium metal plating out at the cathode to form additional Grignard reagent and to prevent short circuiting; it materially increases electrolyte conductivity, thereby reducing power losses; it avoids undesirable side reactions; and increases current efficiency well beyond the theoretical 100 percent, perhaps through the formation of lead dialkyl which requires only two Faradays of electricity per mole of product, which then reacts chemically with Grignard reagent and excess alkyl halide to form the tetra-alkyl lead product. A free alkyl halide concentration of 1-50 percent based on total electrolyte is accordingly representative of optimum practice.

The electrolysis may be conducted batchwise, continuously, or using any combination of modification of these methods. Temperatures in the electrolytic cells are advantageously within the range of about to about 100 C., preferably about -70 C., optimally about -60 C. Anode and cathode current densities are each desirably within the range of about 0.2 to about 25 amperes per hour per square foot. Cell pressures may range from atmospheric to high super-atmospheric-up to about 300 p.s.i.g. or even higher.

Electrolysis is best continued until the alkyl Grignard reagent concentration is below about 1.0 Normal, and for economic reasons is optimally conducted until the concentration is within the range of about 0.2-0.5 Normal. The slight tetra-alkyl lead compound yield increase which may be obtained by continuing the electrolysis normally is outweighed by higher power requirements due to lower electrolyte conductivity at low Grignard concentrations.

Turning now to FIGURE 1, an embodiment of the invention employing a parafiin, hexane, to extract tetraethyl lead from a first liquid phase containing the tetraethyl lead, magnesium chloride etherate, unreacted ethyl magnesium chloride, and dibutyl Carbitol is shown.

Ethyl Grignard is prepared and stored in source 11 at a concentration of 2.79 Normality in dibutyl Carbitol,

The quantity of solution charged from source 11 via line 12 is 36.4 liters.

Electrolysis is conducted in cell 19, containing a plurality of spaced plate electrodes. The anodes 16 are of lead, while the cathodes 17 are of a material which is inert when functioning as the anode, such as stainless steel. Ethyl chloride is added continuously during electrolysis via line 13 until a total of 5440 grams is added. All during the electrolytic reaction, the electrolyte is circulated via lines 21, 22, and 24 and pump 23 to maintain a continuously flowing electrolyte. If desired, heat exchange facilities may be installed in line 24 to permit removal of heat resulting from PR losses and from heat of reaction. When at least a major amount of the alkyl Grignard reagent is converted to tetra-alkyl lead compound and magnesium halide (in this example to tetraethyl lead and magnesium chloride), the electrolyte is withdrawn via line 21 and transferred to surge drum 26. In the present example, Grignard normality is approximately 0.54.

In surge drum 26 excess ethyl chloride is flashed oft" i and taken via overhead line 27 to source 28, from whence it is pumped or compressed back via line 13 to cell 19. It has been discovered that the removal of excess ethyl halide after electrolysis facilitates subsequent separation of the electrolyte into two immiscible liquid phases.

The bottoms from surge drum 26 are pumped via line 29 to settling drum 31. Here the bottoms or ethyl-chloride-free electrolyte is permitted to separate into an upper first liquid phase 32 containing unconverted alkyl Grignard reagent, a minor portion of the tetraethyl lead, magnesium chloride etherate, and excess dibutyl Carbitol ether. The bottom layer 33 contains substantially only tetraethyl lead and ether, e.g., 1.73 molar with respect to tetraethyl lead, about 0.3 molar with respect to Grignard, and about 0.06 molar with respect to magnesium chloride etherate. On the other hand, the upper layer 32 contains only 0.271 mole per liter of tetraethyl lead with 0.69 mole per liter of Grignard, 2.59 moles per liter of total magnesium, and 4.53 moles per liter of total chloride. Lower layer 33 represents 25 volume percent of the electrolyte.

in the embodiment of FIGURE 1, the first or upper layer 32 contains the unreacted Grignard, the magnesium chloride etherate, a minor portion of the tetraethyl lead and ether, while it is the bottom or second layer which contains substantially only tetraethyl lead and the ether. The relative positions of these layers will depend on their relative densities and in turn will be dependent upon the initial composition of the electrolyte and on the extent of electrolysis, together with such other variables as temperatures, etc. Consequently, under some circumstances the densities and hence positions of the first and second layers may be reversed. This however offers no real problem and can be accommodated by simple reversal of the take-cit lines 34 and 41 from settling drum 31.

The first layer is conducted via line 34 to extraction tower 36. This tower may be provided with a plurality of perforated plates to permit the first layer to receive intimate contact by the hexane as the former descends and the latter ascends. Countercurrent contact is most advantageous. Alternatively, tower 36 may be provided with doughnut battles and rotary agitators in each tower section separated by such bafiles. This permits even more efficient contact and extraction, and is especially useful since the denuded first layer becomes quite viscous.

Conditions within tower 36, and the design of tower 36, are selected in view of operational and economic preferences to provide the most advantageous performance. The temperature may be varied widely, e.g., from about 10 to about 120 C., and the ratio of extracting solvent to first layer may vary from about 0.2:1 to about 20:1. Similarly, the number of contact steps in tower 36 (or the height of tower 36 if a packed tower is employed) may also be selected in view of recognized engineering considerations.

The extract phase leaving tower 36 is taken ed at the top via line 38 and passes to distillation tower 61. This extract phase is chiefly hexane and may contain from less than half to as much as percent or more of the tetraethyl lead originally present in the first layer admitted to extraction tower 36. It also contains a trace amount of unreacted Grignard and magnesium chloride etherate, but these ordinarily are not deleterious in the concentrations in which they are present.

In distillation tower 61 the lower boiling hexane is distilled overhead via vapor line 62, condensed by condenser 63, and sent to reflux drum 64. Here a portion of the hexane is returned via line 66 to distillation tower 61 to serve as tower reflux, while another portion is cycled via line 37 to extract tower 36 to repeat the tetraethyl lead extraction step.

The bottoms from distillation tower 61 are largely tetraethyl lead with some unreacted alkyl Grignard reagent, magnesium chloride etherate, and perhaps some ether. This bottoms stream may either be withdrawn via line 68 and treated for tetraethyl lead recovery, as by fractional distillation, or else may be retained in the process as shown in FIGURE 1 by passing the bottoms via line 69 to fractional distillation column 42.

Fractional distillation column 42 contains a plurality of distillation tray's or decks and may be supplied with tetraethyl lead and ether from lines 69 and 41, the latter furnishing the second layer resolved in separation drum 3].. Column 42 may operate either by steam distillation or by vacuum distillation to resolve the tetraethyl leadether solution into its individual components. If vacuum distillation is employed, the column 42 is provided with a rcboiler and other conventional vacuum distillation auxiliaries, e.g., steam jets, etc. However, as shown in the drawing, distillation is advantageously conducted using live steam to obtain the separation. Vacuum distillation may be conducted at pressures from about 5 mm. mercury to about 700 mm. absolute pressure, while steam distillation may be conducted at an absolute pressure of from about 200 mm. pressure to about 50 p.s.i.g.

In the case of steam distillation, live steam, at, say, 30 p.s.i.g. pressure is admitted via line 50 near the bottom of column 42. The vaporous mixture of steam and tetraethyl lead leaves column 42 through vapor line 43 and is condensed by condenser 44 and conducted to reflux drum .6. The upper phase in drum 46 is water, and may be withdrawn via line 47 and discarded, after suitable precautions have been taken to decontaminate the dissolved lead. The heavy layer in drum 46 is taken ofl via line 48 as a tetraethyl lead product of high purity and exeel-lent quality, while a small portion may, if desired, be refluxed to column 4-2 via reflux line 49.

The bottoms from tower 42. consists of moist ether and is conducted via line 51 to cooler 52 and thence to dropout drum 53. Here gross amounts of water are drained off via trap line 54, while the ether passes via line 56 to drier 57. Drier 57 contains a solid drying agent such as adsorbent alumina, silica gel, or a molecular sieve (zeolite) material. The dried ether taken through line 58 may be conducted via line 59' to the Grignard preparation facilities 11.

While the embodiment above described relates to hexane, it will be evident that other hydrocarbons, particulariy the alkanes and cycloalkanes which are liquid at 25 C. and atmospheric pressure, may also be employed. It is preferred that such paraffinic hydrocarbons boil below the boiling point of the tetra-alkyl lead compound being produced so as to facilitate distillative separation. As examples of suitable hydrocarbons there may be mentioned pentanes, hexanes, octanes, decanes, cyclohexane, methylcyclopentane, and mixtures of such paraflins as light virgin naphtha. It is preferred that aromatic compounds be excluded from the extracting solvent as these apparently solubilize the phases undergoing extraction.

Directing attention now to FIGURE 2, an alternative system is shown which employs, in lieu of a paraffinic extracting solvent, a solvent comprising a dialkyl ether of an ethylene gly'col having fewer than three ethylene groups in the glycol portion. It will be noted that the formula of suitable extracting solvent glycol ethers need not exclude the dimethyl ethers, although these are some what less preferred. In a particularly advantageous embodiment of the inventive process, the same glycol ether which is employed to eifect electrolysis is likewise employed for the extraction.

In FIGURE 2, the separation drum 31 corresponds to drum 31 of FIGURE 1, and all other analogous components are similarly numbered identically in the two figures.

The first or top phase 32 in drum 31, containing unconverted Grignard reagent, a minor portion of the tetraethyl lead, magnesium chloride etherate, and dibutyl Carbitol, is conducted via line 34 to extract tower 36. This tower similarly may be a multi-plate, an agitated, or a packed tower. Into the bottom of tower 36 a stream of dibutyl Carbitol is introduced via line 37; the

proportion of extracting solvent to first phase may range from 0.2:1 to about 20: 1. It has been found that under some circumstances a small amount of extracting solvent will dissolve in the first liquid phase, but when the amount of additional solvent is increased, then virtually all of the original extracting solvent may be separated out as an immiscible phase.

Thus, the extract consisting essentially of dibutyl Carbitol and tetraethyl lead leaves tower '36 via line 38 while denuded first liquid phase exhausts via line 39. This latter raffinate may be treated for additional tetraethyl lead and glycol ether recovery by hydrolyzing with an aqueous acid, the amount of acid being at least the quantity necessary to convert all of the magnesium to a magnesium salt. A hydrolyzed solution of this nature will form two phases; one containing the glycol ether and tetraethyl lead while the other contains aqueous magnesium salt. Hydrochloric acid is most convenient for the hydrolysis.

The extract from the tower 36 leaving through line 38 is then conducted to a distillation tower 4-2, corresponding exactly to distillation tower 42 of FIGURE 1. The same tower may be employed for resolving the extract as is used for resolving the second liquid phase 33 in drum 31, and this embodiment is shown in FIGURE 2, wherein line 41 effects the introduction of second liquid phase 33. Distillation in tower 42 follows the procedures outlined in connection with FIGURE 1.

Alternative glycol ethers which may be employed as extracting solvents include dimethyl Cellosolve, diethyl Cellosolve, dibutyl Cellosolve, dimethyl Carbitol, diethyl Carbitol, dibutyl Carbitol, and hexylethyl Carbitol. In any case when the extracting solvent is the same solvent as used in the electrolysis, dried solvent from line 58 may be conducted both via line 59 to Grignard preparation facilities 11 and through line 37 to the extraction tower 36.

Example I In this example a first liquid phase separated from a Grignard electrolysis is extracted with hexane. Extraction is effected batchwise, and although this is not the preferred technique it well illustrates the eifectiveness of the inventive process.

Electrolysis is effected of a 2.79 Normal ethyl magnesium glycol solution in dibutyl Carbitol and containing approximately 10 percent excess ethyl chloride at all times. The final electrolyzed solution is approximately .69 Normal. This electrolyzed electrolyte is permitted to separate into two phases at 25 C. after excess ethyl chloride is removed. The first phase comprises 6.02 parts of a solution of unconverted Grignard reagent, tetraethyl lead, magnesium chloride etherate and excess ether. About 2.48 parts of the second liquid layer, comprising essentially only tetraethyl lead and ether is removed separately.

A gram portion of the first or upper liquid layer is shaken in a separatory funnel with six portions of about 55 cc. each of hexane. Separation of phases is immediate at about 25 C. After each extraction the hexane upper phase is removed.

The six extracts are combined and concentrated by distillation at atmospheric pressure. Analysis showed 14.2 grams of tetraethyl lead in the extract phase, with a trace of dibutyl Carbitol being present. The raflinate contains approximately 0.03 gram of TEL, representing a recovery of 98 percent.

Example II In this example a portion of the electrolyzed electrolyte used for Example I is extracted with dibutyl Carbitol. Again, the extraction is batchwise, and the exceptional high extraction efliciency indicates the potential of a more efficient, continuous and countercurrent extraction.

A 139 gram quantity of the first liquid phase is shaken with 31 grams of dibutyl Carbitol; the mixture becomes homogeneous. A second portion of dibutyl Cmbitol weighing 31 grams is added, and again the mixture remains homogeneous. Finally a 28 gram portion is added, and 65.3 grams of an upper extract phase separates out. This first extract contains 7.98 grams of tetraethyl lead.

The rai'finate is extracted with 4-7 grams of dihutyl Carbitol, and 58.7 grams of extract containing 3.61 grams of tetraethyl lead is recovered.

Extraction is again repeated with 47 grams of dibutyl Carbitol, and 54.0 grams of extract containing 1.51 grams of TEL is obtained.

For a fourth extraction, 38 grams of dibutyl Carbitol is added and 37.5 grams of extract containing 0.46 gram of TEL is obtained.

The total tetraethyl lead recovery is 13.56 grams. Analysis of the rafiinate shows that only 1.26 grams of tetraethyl lead is not recovered.

The extract phase shows very little titratable alkalinity. Similarly, the titratable chloride ion is quite low, indicating that magnesium chloride and Grignard reagent are not appreciably extracted.

In this example, 91.5 percent of tetraethyl lead present is readily extracted with dibutyl Carbitol at 25 C.

The invention has been specifically embodied in a process for the manufacture of tetraethyl lead. Thus, while the process has been described in considerable detail in conjunction with specific embodiments, it is evident that many alternatives, modifications and variations may be employed. Accordingly it is intended to embrace all such alternatives, modifications and variations as fall within t .e spirit and broad scope of the appended claims.

I claim:

1. In a process wherein an electrolyte comprising an alkyl Grignard reagent, excess alkyl halide, and a solvent comprising a dialkyl ether of an ethylene glycol having fewer than 3 ethylene groups in the glycol portion and having at least 2 carbon atoms in each alkyl group is electrolyzed with a lead anode to produce a tetra-alkyl lead compound and magnesium halide, the improved method of recovering the tetra-alkyl lead compound which comprises: separating the electrolyzed electrolyte into two immiscible liquid phases, the first phase containing unconverted Grignard reagent, a minor portion of the tetraalltyl lead compound, magnesium halide etherate, and ether, and the second phase containing substantially only tetra-alkyl lead compound and ether; extracting tetra-alkyl lead compound from said first phase with a solvent selected from the group consisting of paraifins, dialkyl ethers of ethylene glycols having fewer than 3 ethylene groups in the glycol portion, and mixtures thereof; recovering tetraalkyl lead compound from the extract; and recovering additional tetra-alkyl lead compound from the second phase.

2. Process of claim 1 wherein said alkyl Grignard reagent is methyl magnesium chloride.

3. Process of claim 1 wherein said alkyl Grignard reagent is ethyl magnesium chloride.

4. Process of claim 1 wherein said dialltyl ether of an ethylene glycol in said electrolyte is dibutyl ether of diethyleue glycol.

5. Process of claim 1 wherein said dialkyl ether of an ethylene glycol in said electrolyte is ethylhexyl ether of diethylene glycol.

6. Process of claim 1 wherein the initial concentration of alkyl Grignard reagent prior to electrolysis is within the range of about 1.5 to about 3.5 Normal and the concentration after electrolysis is less than about one Normal.

7. Process of claim 1 wherein excessive alkyl halide is removed from the electrolyte after electrolysis and prior to separation of the two liquid phases.

8. Process of claim 1 wherein said extracting solvent is a paramn.

9. Process of claim 8 wherein said paratlin is a normally liquid paratfin boiling lower than the tetra-alltyl lead compound.

10. Process of claim 9 wherein said parafiin is hexane.

11. Process of claim 1 wherein said extracting solvent is a dialkyl ether of an ethylene glycol having fewer than 3 ethylene groups in the glycol portion.

12. Process of claim 1.1 wherein said ether is dibutyl ether of diethylene glycol.

13. Process of claim 12 wherein said ether is the ethylhexyl ether of diethylene glycol.

14-. Process of claim 1 wherein said extracting solvent is a paratfin and wherein the tetra-alkyl lead compound is recovered from the extract by distillation.

15. Process of claim 1 wherein said extracting solvent is a dialkyl ether of an ethylene glycol having fewer than 3 ethylene roups in the glycol portion, and the tetraalkyl lead compound is recovered from the extract by vacuum distillation.

16. Process of claim 1 wherein said extracting solvent is a diallryl ether of an ethylene glycol having fewer than 3 ethylene groups in the glycol portion, and the tctra-alkyl lead compound is recovered from the extract by steam distillation.

17. Process of claim 1 wherein said tetra-alkyl lead compound is recovered from said second liquid phase by distillation.

References Cited in the file of this patent UNITED STATES PATENTS Givaitis July 12, 1960 Braithwaite Nov. 7, 1961 OTHER REFERENCES 

1. IN A PROCESS WHEREIN AN ELECTROLYTE COMPRISING AN ALKYL GRIGNARD REAGENT, EXCESS ALKYL HALIDE, AND A SOLVENT COMPRISING A DIALKYL ETHER OF AN ETHYLENE GLYCOL HAVING FEWER THAN 3 ETHYLENE GROUPS IN THE GLYCOL PORTION AND HAVING AT LEAST 2 CARBON ATOMS IN EACH SLKYL GROUP IS ELECTROLYZED WITH A LEAD ANODE TO PRODUCE A TETRA-ALKYL LEAD SOMPOUND AND MAGNESIUM HALIDE, THE IMPROVED METHOD OF RECOVERING THE TETRA-ALKYL LEAD COMPOUND WHICH COMPRISES: SEPARATING THE ELECTROLYZED ELECTROLYTE INTO TWO IMMISCIBLE LIQUID PHASES, THE FIRST PHASE CONTAINING UNCONVERTED GRIGNARD REAGENT, A MINOR PORTION OF THE TETRAALKYL LEAD COMPOUND, MAGNESIUM HALIDE ETHERATE, AND ETHER, AND THE SECOND PHASE OCNTAINING SUBSTANTIALLY ONLY TETRA-ALKYL LEAD COMPOUND AND ETHER; EXTRACTING TETRA-ALKYL LEAD COMPUND FORM SAID FIRST PHASE WITH A SOLVENT SELECTED FROM THE GOUP CONSISTING OF PARAFIINS, DIALKYL ETHERS OF ETHYLENE GLYCOLS HAVING FEWER THAN 3 ETHYLENE GROUPS IN THE GLYCOL PORTION, AND MIXTURES THEREOF; RECOVERING TETRAALKYL LEAD COMPOUND FROM THE EXTRACT; AND RECOVERING ADDITIONAL TETRA-ALKYL LEAD COMPOUND FROM THE SECOND PHASE. 